High-Flow Nasal Cannula System

1. What is a High-Flow Nasal Cannula (HFNC)?
2. How does a High-Flow Nasal Cannula Work?
3. Precise Oxygen Delivery
4. Fisher & Paykel Airvo 2
5. Final Thoughts

What is a High-Flow Nasal Cannula (HFNC)?

A high-flow nasal cannula (HFNC) system is a heated, humidified device that delivers a prescribed fraction of inspired oxygen (FIO2) at very high flow rates. The main intended uses of HFNC are precise oxygen delivery, improved gas exchange, significant reduction in the work of breathing, and the creation of a reservoir of high F_IO₂ in the nasal cavity.

How does a High-Flow Nasal Cannula Work?

HFNC is delivered using an air/oxygen blender, an active humidifier, a single heated tube, and a nasal cannula. HFNC can warm (to 98.6°F or 37 °C) and humidify the gas, which can decrease airway inflammation, maintain mucociliary function, improve mucous clearance, and reduce caloric expenditure in acute respiratory failure.

The HFNC can also deliver adequately heated and humidified medical gas at flows up to 60 L/min. An HFNC, such as the Fisher & Paykel Airvo 2, is considered to have several physiological advantages over other standard oxygen therapies.

Precise Oxygen Delivery

Traditional nasal cannula systems deliver flow rates of 2–6 L/min. However, patients with respiratory distress can have much higher peak inspiratory flow rates, which can cause the patient to entrain room air into the lungs. This can result in oxygen dilution, and the patient will not receive the desired amount of oxygen.

When an HFNC system is used to deliver oxygen, the flow rates are much higher, resulting in greater delivery of prescribed oxygen into the lungs.

Lastly, when HFNC is applied, the constant high flow of oxygen provides a “washout” of the anatomical dead space of the oropharynx and proximal tracheobronchial tree, which results in more efficient breathing.

Putting the HFNC System to Use

The main adult indications include hypoxemic respiratory failure due to pneumonia, post-extubation, pre-oxygenation prior to intubation, acute pulmonary edema, and use in patients who are “do not resuscitate or intubate”. The main pediatric indication in infants is bronchiolitis, but other indications are being studied, such as its use in asthma, croup, pneumonia, transport of a critically ill child, and post-extubation.

Fisher & Paykel Airvo 2 Features

A perfect example of a high-flow system is the Fisher and Paykel Airvo 2. This humidifier has an integrated flow generator that delivers high-flow, warmed, humidified respiratory gases to spontaneously breathing patients via a variety of patient interfaces. The Airvo 2 is suitable for hospitals and long-term care facilities.

• Dual spiral heated breathing tube with an integrated temperature sensor.
• Use with Optiflow nasal cannula interfaces, direct-connect tracheotomy, and mask interfaces.
• Oxygen from a concentrator or cylinder is optionally added.
• Built-in ultrasonic analyzer requires no calibration, service, or replacement.
• Adjustable temperature and flow settings.
• Designed for simple setup, use, and cleaning.

Fisher & Paykel Airvo 2 Specifications

Dimensions

• Height: 11.6” (29.5 cm)
• Width: 6.7” (17 cm)
• Depth: 6.9” (17.5 cm)
• Weight: 4.8 lbs (2.2 kg)

General

• Supply frequency: 50-60 Hz
• Supply voltage/current: 100-115 V 2.2 A (2.4 A max†); 220-240 V 1.8 A (2.0 A max)
• Sound pressure level: Alarms exceed 45 dB(A) @ 1 m
• Auditory alarm pause: 115 seconds
• Expected service life: 5 years
• Serial port: The serial port is used for downloading product data, using the F&P Infosmart software.
• Warm-up time: 10 minutes to 31 °C (88 °F), 30 minutes to 37 °C (98.6 °F) using a
• MR290 chamber with flow rate of 35 L/min and starting temperature 23 ± 2 °C (73 ± 3 °F)
• Target temperature settings: 37, 34, 31 °C

Performance

• • Humidity performance
    • >33 mg/L at 37 °C target
    • >12 mg/L at 34 °C target
    • >12 mg/L at 31 °C target
  • Maximum temperature of delivered gas: 43 °C (109 °F) (in accordance with ISO 80601-2-74)
  • Maximum surface temperature of applied parts: 44 °C (111 °F) (in accordance with ISO 80601-2-74)
  • Flow range (default): 10-60 L/min
  • Flow range (Junior Mode): 2-25 L/min
  • Maximum oxygen input: 60 L/min

• Oxygen analyzer accuracy: < ± 4 % (within the range 25-95% O2)
• Operating conditions: 18-28 °C (64-82 °F), 30-70% RH

Final Thoughts

Physicians have been using it for a wide variety of underlying diseases and conditions. HFNC oxygen delivery has already proven its value as an effective mode of noninvasive ventilatory support and has been gaining attention as a simple, well-tolerated alternative for respiratory support in critically ill patients.